The present invention relates to a camera of the automatic aperture control type, and more particularly, to a camera of the automatic aperture control type adapted to drive a diaphragm provided on an interchangeable taking lens barrel from a camera body side.
When an automatic exposure of the shutter speed priority type or the program type is effected with a camera on which an interchangeable taking lens barrel (hereinafter referred to simply as an interchangeable lens) is mounted, it is necessary to make a proper calculation based on signals which are detected as by a TTL photometric apparatus provided on a camera body, to transmit a calculated aperture to the interchangeable lens and to then set a diaphragm of the interchangeable lens to the calculated aperture.
As means for transmitting the calculated aperture, it is prevalent that a stop-down member provided on the camera body to be activated by a shutter release operation and a diaphragm lever provided on the interchangeable lens for operating the diaphragm are both interconnected with each other so that the aperture calculated on the camera body side is transmitted to the interchangeable lens. However, when the stop-down member or the diaphragm lever is operated, the relationship between a rotational angle thereof and an F number of the interchangeable lens varies depending upon the interchangeable lens. Specifically, the relationship is not in a linear proportion as shown in curves a.sub.0, b.sub.0 (FIG. 1A) or has the different properties as shown in the curve a.sub.0 or b.sub.0 according to interchangeable lenses. Thus, this difference is caused between the rotational angle of the stop-down member and an aperture obtained thereby (that is, a real aperture) for each interchangeable lens. In other words, even when the calculated aperture is set to the interchangeable lens, the aperture can not be set into another interchangeable lens. To overcome the disadvantage, a special device must be planned that when the stop-down member or the diaphragm lever is rotated, the relationship between the rotational angle and F number is made in a linear proportion, as shown in FIG. 1B, and the diaphragm is set just as calculated even when an interchangeable lens is changed. Alternatively, an interchangeable lens must be employed which has a separate mount capable of effecting an aperture control of the shutter speed priority type or the program type. Accordingly, even when a camera body of either the shutter speed priority type or the program type is newly procured utilizing an interchangeable lens of only the conventional aperture priority type, the combination of the interchangeable lens and the camera body can not satisfy the essential functions of the shutter speed priority type or the program type.
Furthermore, as shown in FIG. 2A, even when a proper aperture is calculated as by TTL photometry, a proper exposure is not performed due to a time lag in the follow-up operation of the stop-down member or a time lag in operation of the stop-down member after a terminate signal is given thereto. For example, even when an exposure is to be made with a proper aperture as indicated by a point "A.sub.1 ", it may be made in practice with a different aperture as indicated by a point "A.sub.2 ".